Laser pointers are used both indoors and outdoors. In outdoor use, laser pointers are used to draw attention to particular objects and terrain features. In some outdoor applications, in order to be useful, the laser spot on the illuminated area must be visible from at least 100 meters from the laser spot, and preferably at even greater distances.
At night, even low power, eyesafe laser pointers are sufficient to effectively draw attention when the person observing the laser spot is hundreds of meters from the laser spot. However, during daytime, the laser pointer must have much higher power in order to be visible at distances of 100 meters or more from the laser spot. The reason that high laser pointer output power is needed during the day is that the detection of the laser pointer spot is more difficult when the observer must pick the spot out from the sunlit background.
An additional application of laser pointers is their use by police and military personnel to attract the attention of drivers, in order to allow the police and military personnel to conduct security operations at locations such as highway checkpoints. In this use, higher laser powers are required, especially during the day, in order to assure that drivers of vehicles can be reliably notified by the presence of laser radiation that they are being addressed by the police or military; failure of notification in these situations can have fatal consequences if the driver does not see or recognize the notification provided by the laser pointer. This tends to motivate increases in the power of laser pointers used at such checkpoints.
In those cases in which the beam profile of the laser system has been designed to cover an extended angular area, it is more appropriate to refer to it as a laser illuminator rather than as a laser pointer. These cases may include the use of laser systems by police and military personnel in situations in which it is desired that an area, such as the area of a vehicle windshield, be entirely illuminated by the laser system, rather than only a single small part of the vehicle windshield.
One of the problems with using laser pointers and laser illuminators that produce high optical output power is that such laser pointers and laser illuminators have the capability to produce eye injuries when the pointer or illuminator is accidentally pointed directly into any person's eye from short range. This limits the usefulness of pointers and illuminators used outdoors, especially during the day, because pointer or illuminator optical output power must be restricted in order to keep the risk of accidental eye injuries at an acceptably low level.
To allow the use of laser pointers and laser illuminators at desired ranges, it is necessary to protect personnel from accidental exposure to the beam directly from the laser pointer or laser illuminator. Prior art provides the possibility of incorporating optical filtering into eyewear so that radiation at the wavelength of the laser is blocked, while radiation at other wavelengths is passed by the spectral filter that is included in the eyewear. This prevents eye injuries, while still allowing normal vision through the eyewear. Although this prior art provides protection of personnel wearing appropriately designed eyewear from injuries from laser pointers and laser illuminators, it also defeats one of the purposes of the laser pointer or laser illuminator because not only is radiation blocked when a laser pointer or laser illuminator is accidentally pointed directly at a person wearing such eyewear, it is also blocked when such a person is attempting to see the laser spots or illuminated areas produced by his/her or another's laser pointer or laser illuminator on illuminated objects or terrain features.
To allow operation of laser pointers and laser illuminators outdoors at useful ranges, with low risk of eye injury, it would be highly desirable if the pointer or illuminator and the associated eyewear were such that a direct beam from any pointer or illuminator is blocked by the eyewear, but beams reflected from diffuse objects such as buildings, vegetation, and terrain are visible through the eyewear. This would eliminate eye injuries due to pointers and illuminators pointed directly at the eyes of persons wearing such eyewear, while still allowing observation of laser radiation scattered from diffuse objects. For example, if a group of soldiers or police are manning a checkpoint, and all members of the police or military group are wearing suitable eyewear, then fratricide eye injuries (i.e. injuries due to one soldier or policeman accidentally pointing a laser pointer or laser illuminator into his own eye or the eye of another soldier or policeman at short range) would be completely eliminated.
Furthermore, for additional degree of protection, a nearly collimated beam from a laser pointer can be electronically switched to an illuminator mode, in which a liquid crystal (LC) based device with diffractive waveplate structure as disclosed by Tabiryan et al. in Optics and Photonics News, 21 (3), 41-45, 2010 (N. V. Tabiryan, S. R. Nersisyan, D. M. Steeves and B. R. Kimball, The Promise of Diffractive Waveplates) will be switched to create an extended source that would drastically reduce the distance from the laser pointer at which the laser pointer is an eye hazard and significantly improve its eyesafety characteristics. The switching LC element would allow to switch between multiple states to create various beam profile distributions, divergences not only for eye-safety purposes but also for adapting the pointing/illumination conditions for optimal observation of the pointer/illuminator beam. The switchable LC elements can have a structure of an array of microlenses and phase distribution plates designed to output desired beam profile due to modulation of optical axis orientation of the LC.
Laser pointers and laser illuminators also have the capability to produce damage in optical sensors other than eyes designed to see the spots from laser pointers or objects illuminated by laser illuminators. Thus, it would be useful to provide protection of such other optical sensors from damage by the direct beam from laser pointers and from laser illuminators.
Thus, the need exists for solutions to the above problems with the prior art.